The present invention relates to a process for producing tension members and more especially for producing corrosion-resistant parallel wire cables. For the construction of large-span cable stayed bridges of steel or reinforced concrete and for similar structural applications, and also for reactor construction, tension members with an especially high carrying capacity are required. They can be produced as bundles of an appropriately large number of parallel arranged wires.
Wires or stranded wires with a greater cross-section than customarily used up until now (7 to 10 mm diameter with nominal tensile strengths of 1600 to 1800 N/mm.sup.2) should be used with the objective of obtaining a allowable load strength of at least 1000 Mp (1000 KN). For this purpose, the following operating steps can be carried out without difficulties by using a newly developed process, which comprises the steps of:
a. Winding such heavy parallel wire bundles up on reels in the central fabrication plant, after the anchoring members have already been cast there, in order to assure reliably equal wire lengths within the individual bundles; and
b. Unwinding of the parallel wire bundles at the construction site, following transportation, so that the individual wires must not sustain, in this process, any edge damage or tensions which exceed the elastic limit. See U.S. Pat. No. 3,919,762, the disclosure of which is hereby incorporated by reference.
In order to make possible an economical application of these high-performance tension members in large bridge constructions, especially in the construction of cable stayed bridges, it is necessary to be able to produce a reliable protection against corrosion with sufficient resistance against longterm influences of unconstrained weathering.
To date, no completely satisfactory corrosion protection measures have become known, particularly none which are sufficiently effective against attacks from the atmosphere in the case of waste-gas-producing industry. In addition, known measures can usually only be finally carried out after assembly of the tension members is completed in the exposed position, namely, in the air from suspended baskets, scaffolds, or cable gangways (rat worms), with a high labor cost and with interference from unfavorable weather influences. This makes it difficult to perform a continuous careful monitoring of the work which is carried out.
To date, considerable damage after the passage of a certain amount of time has been found on the corrosion protecting coatings of paints, lacquers, and synthetic resins, which appeared especially suitable for an economical implementation for reasons of price and quality, due to the influence of the ultraviolet rays, as well as the especially disadvantageous influences of the oxygen in the air with sun radiation and at higher temperatures. The life span of these corrosion protection coatings is thus reduced to a degree which has so far been controllable with difficulty in practice. The repair of the tension members, which are located in an exposed position, is difficult and very costly.
Added to this is the fact that the penetration of moisture, especially of gases, into the initially still undamaged synthetic skin by diffusion, as well as of aggressive liquids into the cracks which form with time, and thus the beginning of the corrosion on the very sensitive high-strength wires can be reliably monitored only with difficulty. This is particularly very critical because, as is known, an embrittlement of the material occurs in the course of time in the case of synthetic materials, which are exposed to open weather, particularly those of the group of thermoplastics, even with the addition of carbon black, and the notches which develop on the surface further propagate as cracks toward the inside in the case of any mechanical stresses which may occur.
In order to be able to determine if and when a destruction has occurred on the inside of the parallel wire bundles, a constant careful and thus costly individual in situ control must be carried out after a certain number of years following installation. A reliable method is not yet known for this. It is therefore an urgent requirement to find a corrosion protection process which enables a life span of the parallel wire bundles which at least corresponds to, if not exceeds, that of the bridge which is supported by this tension members. Even higher expenses in the production of these corrosion protected parallel wire bundles appear to be justified if it is possible to avoid the previous uncertainty with respect to the life span of these tension members, the necessity for a constant careful monitoring, as well as the relatively high repair costs.
Therefore, a process which makes it possible to apply such a corrosion protection of the tension members, especially of the parallel wire bundles, prior to the completion of the assembly, at the construction site, under a small protective roof, appears to be especially advantageous. Here, a technically adequate quality control of the corrosion protection can be carried out. Under these conditions, the investment for constantly reusable, easily transporable apparatus which is necessary for the implementation of the corrosion protection process, as well as for a special installation process which is necessary for these protected tension members, is also justified economically.
Some proposals for a corrosion protection for parallel wire bundles are already available, see, e.g., DT-OS No. 23 57 006, as well as Japanese application No. 100,346/75 and U.S. Pat. No. 3,919,762. However, certain further developments have, in part, proven to be significant in practical application. In particular, they could be improved with respect to an effective long-term protection against weather influences.